Collaborative Research: Evaluation of Cumulus Petrofabrics Using Magnetic Fabrics

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9902895GeeThe fabrics of cumulus rocks preserve the only direct evidence of the mechanical processes involved in fractional crystallization of silicate liquids. Quantification of these igneous fabrics and understanding their origin is critical since the mechanical processes that give rise to the fabrics have chemical as well as textural consequences. Because quantitative petrographic studies of fabrics are time consuming, we propose to use cumulates from the Stillwater complex, Montana to develop an approach for relating magnetic fabrics (that are sensitive to both the orientation of magnetic minerals as well as the silicate minerals) to silicate fabrics in ultramafic and mafic cumulates. These magnetic methods have the advantage of providing direct 3D fabric information, having precision to detect small degrees (~0.5%) anisotropy, and being rapid enough to collect fabric data from a large number of samples. Our initial results suggest that these magnetic techniques provide accurate information on magmatic foliations and, in some cases, recover lineations that are not evident from petrographic analysis alone. If igneous fabrics can be analyzed and quantified in the systematic manner that geochemical data are collected, then studies of cumulates will progress past the point of speculating as to the importance of mechanical processes to documenting their importance.